The common practice in forming fibers of mineral material is to pass the material in a molten state through the orifices of the peripheral wall of a centrifuge or spinner to create primary fibers. Thereafter, the primary fibers are further attenuated into a veil of secondary fibers of smaller diameter by the action of a flow of gases discharged downwardly from an annular blower. It is known that a passageway can be provided over the top of a blower for the introduction of induced air by the blower jet. The induced air flow turns the primary fibers downwardly and brings them into contact with the blower jet. Typically, the blower jet induces four times its own air flow.
One of the problems associated with the blowers of the fiber forming devices of the prior art is that the induced air is typically made to follow the contour of the cap of the blower, which requires the induced air to make sharp changes in direction. This has a destabilizing effect on the flow pattern causing undue fluctuation in the flow field of the induced air. This fluctuation is translated to the fibers, causing them to run into each other and fuse, degrading product quality.
Another problem with conventional annular blowers for mineral fiberizers is that the blowers are somewhat inefficient. Typically, the blower outlet is positioned at the level of the top row of orifices in the spinner, but the fibers do not reach the blower jet until a position well below the spinner is attained. Although the flow of induced air is helpful in turning the fibers downwardly, it causes a delay in the time for the fiber to reach the blower jet. Since the blower jet decays rapidly as it moves downwardly, the full efficiency of the blower jet is not applied to the glass fibers. This problem is made worse by the trend toward finer fibers which have a lower momentum, and for which it is even more difficult to penetrate the induced air flow and reach the influence of the blower jet.
There is a need for a blower which provides for an induced air flow which is more stable and is more easily penetrated by the mineral fibers. Also, there is a need for a blower of greater efficiency which can influence and attenuate mineral fibers closer to the blower outlet.